Light emitting device and method of manufacturing the same

ABSTRACT

A high-quality light emitting device is provided which has a long-lasting light emitting element free from the problems of conventional ones because of a structure that allows less degradation, and a method of manufacturing the light emitting device is provided. After a bank is formed, an exposed anode surface is wiped using a PVA (polyvinyl alcohol)-based porous substance or the like to level the surface and remove dusts from the surface. An insulating film is formed between an interlayer insulating film on a TFT and the anode. Alternatively, plasma treatment is performed on the surface of the interlayer insulating film on the TFT for surface modification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device with a lightemitting element composed of an anode, a cathode, and a film thatcontains an organic compound capable of emitting light upon applicationof electric field (the film is hereinafter referred to as organiccompound layer), and to a method of manufacturing the light emittingdevice. Specifically, the present invention relates to a light emittingdevice using a light emitting element that is lower in drive voltage andlonger in element lifetime than conventional ones. A light emittingdevice in this specification refers to an image display device that usesa light emitting element. Also, the following modules are all includedin the definition of the light emitting device: a module obtained byattaching to a light emitting element a connector such as an anisotropicconductive film (FPC: flexible printed circuit), a TAB (tape automatedbonding) tape, or a TCP (tape carrier package); a module in which aprinted wiring board is provided at an end of a TAB tape or a TCP; and amodule in which an IC (integrated circuit) is directly mounted on alight emitting element by the COG (chip on glass) method.

2. Description of the Related Art

Light emitting elements are drawing attention as the next-generationflat panel display elements for their characteristics including beingthin and lightweight, fast response, and direct current low voltagedriving. Also, being self-luminous and having wide viewing angle givethe light emitting elements better visibility. Therefore the lightemitting elements are considered as effective elements for displayscreens of electric appliances and are being actively developed.

It is said that light emitting elements emit light through the followingmechanism: a voltage is applied between electrodes that sandwich anorganic compound layer, electrons injected from the cathode and holesinjected from the anode are re-combined at the luminescent center of theorganic compound layer to form molecular excitons, and the molecularexcitons return the base state while releasing energy to cause the lightemitting element to emit light. Molecular excitons generated in organiccompounds take either singlet excitation or triplet excitation. Thisspecification deals with elements that emit light from singletexcitation and elements that emit light from triplet excitation both.

These light emitting elements are classified by driving methods intopassive matrix (simple matrix) type and active matrix type. The onesthat are attracting attention most are active matrix type elements, forthey are capable of displaying images of high definition with the QVGAlevel number of pixels or more.

An active matrix light emitting device having a light emitting elementhas an element structure as the one shown in FIG. 2. A TFT 202 is formedon a substrate 201 and an interlayer insulating film 203 is formed onthe TFT 202.

On the interlayer insulating film 203, an anode (pixel electrode) 205 isformed to be electrically connected to the TFT 202 through a wiring line204. A material suitable for the anode 205 is a transparent conductivematerial having a large work function. An ITO (indium tin oxide) film, atin oxide (SnO₂) film, an alloy film of indium oxide and zinc oxide(ZnO), a semi-transparent gold film, a polyaniline film, etc. areproposed. Of those, the ITO film is used most because it has a band gapof about 3.75 eV and is highly transparent in the range of visiblelight.

An organic compound layer 206 is formed on the anode 205. In thisspecification, all the layers that are provided between an anode and acathode together make an organic compound layer. Specifically, theorganic compound layer 206 includes a light emitting layer, a holeinjection layer, an electron injection layer, a hole transporting layer,an electron transporting layer, etc. A basic structure of a lightemitting element is a laminate of an anode, a light emitting layer, anda cathode layered in this order. The basic structure can be modifiedinto a laminate of an anode, a hole injection layer, a light emittinglayer, and a cathode layered in this order, or a laminate of an anode, ahole injection layer, and a light emitting layer, an electrontransporting layer, and a cathode layered in this order.

After the organic compound layer 206 is formed, a cathode 207 is formedto complete a light emitting element 209. The cathode is often formed ofa metal having a small work function (typically, a metal belonging toGroup 1 or 2 in the periodic table). In this specification, such metal(including alkaline metals and alkaline earth metals) is called analkaline metal.

A bank 208 is formed from an organic resin material to cover the edgesof the anode and prevent short circuit between the anode and the cathodeat the site.

FIG. 2 shows one pixel and the light emitting element formed therein.The actual pixel portion is provided with a plurality of light emittingelements each structured as shown in FIG. 2 to constitute an activematrix light emitting device.

In the above-described conventional structure for a light emittingdevice, the interlayer insulating film and the anode (transparentconductive material) formed on the interlayer insulating film havedifferent thermal expansion coefficients. When heat treatment isperformed on a structure in which materials having different thermalexpansion coefficients are in contact with each other as in thisconventional light emitting device structure, it causes a crack in theinterface on the side of the material that has the smaller thermalexpansion coefficient (the anode, in this case). The anode is anelectrode for injecting holes that participate in light emission intothe organic compound layer. If there is a crack in the anode, the crackaffects generation of holes, reduces the number of holes injected, andeven degrades the light emitting element itself. The irregularities ofthe surface of the anode also affect generation and injection of holes.

Furthermore, the organic compound layer is by nature readily degraded byoxygen and moisture. Despite this fact, organic resin materials such aspolyimide, polyamide, and acrylic are frequently used to form theinterlayer insulating film and oxygen or other gas released from thisinterlayer insulating film degrades the light emitting element.

Moreover, the cathode of the light emitting element is formed of analkaline metal material, such as Al or Mg, which can seriously impairTFT characteristics. An alkaline metal mixed in an active layer of a TFTcauses a change in electric characteristic of the TFT, making itimpossible to give the TFT a long-term reliability.

In order to avoid impairing TFT characteristics, it is preferable toprevent alkaline metal contamination of an active layer of a TFT byseparating a TFT manufacture step processing room (clean room) from alight emitting element manufacture step processing room (clean room).However, another problem arises when moving a substrate between rooms(clean rooms) is added to the manufacture process in order to preventthe alkaline metal contamination; the TFT substrate may be contaminatedby dusts or other contaminants in the air, and the TFT element may bedamaged by electrostatic discharge.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide ahigh-quality light emitting device having a long-lasting light emittingelement that is free from the problems described above because of astructure that allows less degradation than conventional ones, and toprovide a method of manufacturing the light emitting device.

The present invention is characterized in that: an interlayer insulatingfilm is formed on a TFT that is formed on an insulator; an insulatingfilm is formed on the interlayer insulating film; an anode is formed tobe electrically connected to the TFT through a wiring line; a resininsulating film is formed to cover the anode and the wiring line; theresin insulating film is etched to form a bank; the anode iswiped/cleaned after heat treatment; and an insulating film is formed tocover the anode and the bank.

The insulating film formed between the interlayer insulating film andthe anode can suppress the generation of cracking caused by heattreatment in adjoining materials that have different thermal expansioncoefficients. The light emitting element thus can have a long lifetime.This insulating film is also capable of preventing gas or moisturereleased from the interlayer insulating film from reaching the lightemitting element. The insulating film may be an inorganic insulatingfilm, or may be a cured film obtained by surface modification throughplasma treatment or a DLC film.

By wiping the anode, the irregularities of the surface of the anode canbe leveled and dusts on the surface of the anode can be removed.

By forming the insulating film that covers the anode and the bank, aneffect of balancing amounts of holes and electrons to be injected to theorganic compound layer can be expected.

Another aspect of the present invention is characterized in that: aresin insulating film for forming a bank is formed; the substrate ismoved to a processing room where contamination by an alkaline metal orothers can be avoided; and the resin insulating film is etched to formthe bank.

Anti-electrostatic treatment is conducted after the insulating film forprotecting the semiconductor film of the TFT is formed. A firstprocessing room (first clean room) for forming a TFT substrate isseparated from a second processing room (second clean room) for forminga light emitting element. Thus, the risk of an alkaline metal mixing inthe active layer of the TFT from the alkaline metal material forming thecathode of the light emitting element, such as Al or Mg is lowered. As aresult, electric characteristics of the TFT and the long-termreliability thereof can be improved.

The anti-electrostatic film is formed from a material which-does notaffect the resin insulating film for forming the bank, the anode, andthe wiring and can be removed by water washing or like other simplemethods. As such the material, a material having conductivity necessaryfor conducting the anti-electrostatic treatment is suitable (forexample, 10⁻⁸[S/m] or more). An conductive organic material is generallyused, for example, the anti-electrostatic film comprising conductivepolymer is formed by spin coating, and the anti-electrostatic filmcomprising conductive low molecular is formed by evaporation.Concretely, polyethylene dioxythiophene (PEDOT), polyaniline (PAni),glycerin fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylenealkylphenyl ether, N,N-Bis(2-hydroxyethyl)alkylamine [alkyldiethanolamine], N-2-Hydroxyethyl-N-2-hydroxyalkylamine [hydroxyalkylmonoethanolamine], polyoxyethylene alkylamine, polyoxyethylenealkylamine fatty acid ester, alkyl diethanolamide, alkyl sulfonate,alkylbenzenesulfonate, alkyl phosphate, tetraalkylammonium salt,trialkylbenzylammonium salt, alkyl betaine, alkyl imidazolium betaine,or the like are used. These can be easily removed by water or an organicsolvent. In addition, an organic insulating material, such as polyimide,acrylic, polyamide, polyimideamide, or BCB (benzocyclobutene) can beused as the anti-electrostatic film. The anti-electrostatic film formedfrom the material mentioned above can be applied to all embodiments.

Another aspect of the present invention is characterized by comprising astep of forming a bank and performing plasma treatment on the surface ofthe bank after heat treatment is performed on the anode forcrystallization.

A cured film is formed on the surface of the bank through the surfacemodification thereof by plasma treatment. This prevents the bank fromreleasing its moisture and degrading the light emitting element.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1E are diagrams showing a method of manufacturing a lightemitting device in accordance with an embodiment mode;

FIG. 2 is a diagram showing an example of a conventional light emittingdevice;

FIGS. 3A to 3D are diagrams showing a process of manufacturing a lightemitting device;

FIGS. 4A to 4C are diagrams showing a process of manufacturing a lightemitting device;

FIGS. 5A to 5C are diagrams showing a process of manufacturing a lightemitting device;

FIGS. 6A and 6B are diagrams showing a process of manufacturing a lightemitting device;

FIG. 7 is a diagram showing an example of carrying out a light emittingdevice manufacture process;

FIG. 8 is a diagram showing an example of carrying out a light emittingdevice manufacture process;

FIGS. 9A and 9B are diagrams showing a scaling structure for a lightemitting device;

FIGS. 10A and 10B are diagrams showing the structure of a pixel portionof a light emitting device;

FIGS. 11A to 11H are diagrams showing examples of an electric appliance;

FIG. 12 is a diagram showing an example of carrying out a light emittingdevice manufacture process;

FIG. 13 is a diagram showing an example of carrying out a light emittingdevice manufacture process;

FIG. 14 is a diagram showing results of AFM measurement;

FIG. 15 is a diagram showing results of AFM measurement;

FIG. 16 is a diagram showing results of AFM measurement;

FIGS. 17A to 17F are diagrams showing a process of manufacturing a lightemitting device in accordance with an embodiment;

FIGS. 18A and 18B are diagrams showing a process of manufacturing alight emitting device;

FIG. 19 is a conceptual diagram showing a production process of thepresent invention;

FIGS. 20A to 20D are diagrams showing an example of carrying out a lightemitting device manufacture process;

FIGS. 21A to 21C are diagrams showing an example of carrying out a lightemitting device manufacture process; and

FIGS. 22A and 22B are diagrams showing an example of carrying out alight emitting device manufacture process.

FIGS. 23A and 23B are diagrams showing an example of carrying out alight emitting device manufacture process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment Mode

A TFT 101 is formed on a substrate 100. The TFT shown here is a TFT forcontrolling a current flowing into a light emitting element, and iscalled in this specification as a current controlling TFT 101 (FIG. 1A).

On the current controlling TFT 101, an interlayer insulating film 102 isformed for planarization. The interlayer insulating film 102 is formedfrom an organic resin material such as polyimide, acrylic, polyamide,polyimideamide, an epoxy resin, or BCB (benzocyclobutene) to have anaverage thickness of about 1.0 to 2.0 μm. The substrate can be properlyleveled by forming the interlayer insulating film 102. Moreover, theinterlayer insulating film can reduce parasitic capacitance sinceorganic resin materials are low in dielectric constant in general.

Next, a first insulating film 103 is formed on the interlayer insulatingfilm 102 so that gas released from the interlayer insulating film 102does not affect the light emitting element. The first insulating film103 is an inorganic insulating film, typically, a silicon oxide film, asilicon oxynitride film, or a silicon nitride film, or a laminate havingthe above films in combination. The first insulating film is formed byplasma CVD in which the reaction pressure is set to 20 to 200 Pa, thesubstrate temperature is set to 300 to 400° C., and the high frequency(13.56 MHz) power density is set to 0.1 to 1.0 W/cm² for electricdischarge. Alternatively, a cured film containing one or more kinds ofgas elements selected from the group consisting of hydrogen, nitrogen,halogenated carbon, hydrogen fluoride, and rare gas is formed by plasmatreatment performed on the surface of the interlayer insulating film.

Thereafter a resist mask having a desired pattern is formed. A contacthole reaching a drain region of the current controlling TFT 101 isformed to form a wiring line 104. The wiring line is formed from a Alfilm or a Ti film as a conductive metal film, or an alloy film of Al andTi. The material is deposited by sputtering or vacuum evaporation toform a film, and the obtained film is patterned into a desired shape.

A transparent conductive film 105 is formed next to serve as an anode ofthe light emitting layer. The transparent conductive film 105 istypically formed from indium tin oxide (ITO), or from indium oxide with2 to 20% of zinc oxide (ZnO) mixed therein.

The anode is formed by etching the transparent conductive film 105.Thereafter, a bank 107 is formed and heat treatment is conducted at 230to 350° C. In this specification, an insulating film which has anopening above the anode and which covers the edges of the anode iscalled as a bank (FIGS. 1B and 1C)

The surface of the anode 106 is wiped using a PVA (polyvinylalcohol)-based porous substance along with a washing liquid to level thesurface of the anode 106 and remove dusts therefrom. In thisspecification, wiping an anode surface with a PVA (polyvinylalcohol)-based porous substance to level the surface and remove duststherefrom is expressed as wiping.

After wiping the surface of the anode, a second insulating film 110 isformed. An organic compound layer 111 and then a cathode 112 are formedon the second insulating film 110. The second insulating film 110 is apolyimide, polyamide, acrylic, or other organic resin insulating filmformed by spin coating to a thickness of 1 to 5 nm.

The organic compound layer 111 is a laminate that has, in addition to alight emitting layer, a hole injection layer, a hole transporting layer,a hole blocking layer, an electron transporting layer, an electroninjection layer, a buffer layer, etc. in combination. The thickness ofthe organic compound layer 111 is preferably about 10 to 400 nm.

The cathode 112 is formed by evaporation after the organic compoundlayer 111 is formed. The material of the cathode 112 is MgAg or a Al—Lialloy (alloy of aluminum and lithium). Alternatively, the cathode may bea film formed by co-evaporation of an element belonging to Group 1 or 2in the periodic table and aluminum. The thickness of the cathode 112 ispreferably about 80 to 200 nm.

The state of the surface of the transparent conductive film after wipingtreatment is observed by using an atomic force microscope (AFM), and theresults are shown in FIGS. 14 to 16.

The surface observation in this embodiment uses as a measurement surfacean ITO film that is formed to a thickness of 110 nm on a glass substrateand crystallized by heat treatment at 250° C.

FIGS. 14 and 15 show the irregularities of the substrate surfaceobserved by AFM. Shown in FIG. 14 are results of observing a measurementsurface before wiping treatment whereas FIG. 15 shows results ofobserving the measurement surface after wiping treatment.

FIG. 16 shows the average surface roughness (Ra) before and after wipingtreatment using Bellclean (a product of Ozu Corporation) as a PVA-basedporous material for wiping. The average surface roughness here isexpanded three-dimensionally so that the center line average heightdefined by JIS B0601 can be applied with respect to the surface to beobserved. From the results, the average surface roughness on themeasurement surface is reduced and the levelness is increased after thewiping treatment.

Embodiment 1

This embodiment gives a description about a light emitting element thatis manufactured using the present invention. Described here withreference to FIGS. 3A to 6B is an example of a method of manufacturingTFTs for a pixel portion and TFTs (an n-channel TFT and a p-channel TFT)for a driving circuit at the same time on the same substrate. The pixelportion has the light emitting element of the present invention. Thedriving circuit is provided in the periphery of the pixel portion.

First, a glass substrate 900 is prepared. In this embodiment, bariumborosilicate glass, typical example of which is Corning #7059 glass or#1737 glass (product of Corning Incorporated), or alumino borosilicateglass is usable as the substrate 900. The substrate 900 can be anylight-transmissive substrate, and a quartz substrate may also be used. Aplastic substrate may be employed if it has a heat resistance againstthe process temperature of this embodiment.

Next, as shown in FIG. 3A, a base insulating film 901 is formed on thesubstrate 900 from an insulating film such as a silicon oxide film, asilicon nitride film, or a silicon oxynitride film. In this embodiment,the base insulating film 901 has a two-layer structure. However, asingle layer or more than two layers of the insulating films listedabove may be used as the base insulating film. The first layer of thebase insulating film 901 is a silicon oxynitride film 901 a formed to athickness of 10 to 200 nm (preferably 50 to 100 nm) by plasma CVD usingas reaction gas SiH₄, NH₃, and N₂O. The silicon oxynitride film 901 a(composition ratio: Si=32%, O=27%, N=24%, H=17%) formed in thisembodiment has a thickness of 50 nm. The second layer of the baseinsulating film 901 is a silicon oxynitride film 901 b formed to athickness of 50 to 200 nm (preferably 100 to 150 nm) by plasma CVD usingas reaction gas SiH₄ and N₂O. The silicon oxynitride film 901 b(composition ratio: Si=32%, O=59%, N=7%, H=2%) formed in this embodimenthas a thickness of 100 nm.

On the base insulating film 901, semiconductor layers 902 to 905 areformed. The semiconductor layers 902 to 905 are formed by patterninginto a desired shape a crystalline semiconductor film that is obtainedby forming a semiconductor film with an amorphous structure through aknown method (sputtering, LPCVD, plasma CVD, or the like) and thensubjecting the film to known crystallization treatment (e.g., lasercrystallization, thermal crystallization, or thermal crystallizationusing nickel or other catalysts). The semiconductor layers 902 to 905are each 25 to 80 nm in thickness (preferably 30 to 60 nm). The materialof the crystalline semiconductor film is not limited, but silicon or asilicon germanium (Si_(X)Ge_(1-x) (X=0.0001 to 0.02)) alloy ispreferable. In this embodiment, an amorphous silicon film with athickness of 55 nm is formed by plasma CVD and then a solutioncontaining nickel is held to the top face of the amorphous silicon film.The amorphous silicon film is next subjected to dehydrogenation (at 500°C., for an hour), then to thermal crystallization (at 550° C., for fourhours), and then to laser annealing treatment for improvement ofcrystallinity to obtain a crystalline silicon film. Patterning treatmentusing photolithography is conducted on this crystalline silicon film toform the semiconductor layers 902 to 905.

The semiconductor layers 902 to 905 may be doped with a minute amount ofimpurity element (boron or phosphorus) in order to control the thresholdof the TFTs after the formation of the semiconductor layers 902 to 905.

If laser crystallization is used to form the crystalline semiconductorfilm, a pulse oscillating type or continuous wave excimer laser, YAGlaser, or YVO₄ laser can be employed. Laser light emitted by one chosenout of these lasers is preferably collected into a linear beam by anoptical system before irradiating the semiconductor film. Thoughconditions of crystallization can be set suitably by an operator, thereare some preferred conditions. When an excimer laser is used, preferableconditions include setting the pulse oscillation frequency to 300 Hz,and the laser energy density to 100 to 400 mJ/cm² (typically, 200 to 300mJ/cm²). When a YAG laser is used, preferable conditions include usingthe second harmonic thereof, and setting the pulse oscillation frequencyto 30 to 300 kHz and the laser energy density to 300 to 600 mJ/cm²(typically, 350 to 500 mJ/cm²). The laser light is collected into alinear beam having a width of 100 to 1000 μm, 400 μm, for example, toirradiate the entire surface of the substrate with the beam. In theirradiation, the overlap ratio of the linear laser light is set to 50 to90%.

Next, a gate insulating film 906 is formed to cover the semiconductorlayers 902 to 905. The gate insulating film 906 is formed from aninsulating film containing silicon by plasma CVD or sputtering to athickness of 40 to 150 nm. This embodiment uses a silicon oxynitridefilm (composition ratio: Si=32%, O=59%, N=7%, H=2%) formed by plasma CVDto a thickness of 110 nm. The gate insulating film is not limited to thesilicon oxynitride film, of course, but may be a single layer or alaminate of other insulating films containing silicon.

When a silicon oxide film is used for the gate insulating film, the filmis formed by plasma CVD in which TEOS (tetraethyl orthosilicate) and O₂are mixed, the reaction pressure is set to 40 Pa, the substratetemperature is set to 300 to 400° C., and the high frequency (13.56 MHz)power density is set to 0.5 to 0.8 W/cm² for electric discharge. Thesilicon oxide film thus formed can provide excellent characteristics asthe gate insulating film when the film receives subsequent thermalannealing at 400 to 500° C.

A heat-resistant conductive layer 907 for forming a gate electrode isformed on the gate insulating film 906 to a thickness of 200 to 400 nm(preferably 250 to 350 nm). The heat-resistant conductive layer 907 maybe a single layer or a laminate of two, three, or more layers ifnecessary. The heat-resistant conductive layer may be a film containingan element selected from the group consisting of Ta, Ti, and W.Alternatively, the heat-resistant conductive layer may be an alloy filmcontaining one of the elements listed above and other elements, or analloy film containing a combination of the elements listed above.Sputtering or CVD is used to form the heat-resistant conductive layer.In order to reduce the resistance of the layer, the concentration ofimpurities contained in the layer should be lowered and the oxygenconcentration in particular is preferably reduced to 30 ppm or less. Inthis embodiment, a W film is formed to a thickness of 300 nm. The W filmmay be formed by sputtering with W as the target, or by thermal CVDusing tungsten hexafluoride (WF₆). In either case, the W film has tohave a low resistivity in order to use the W film as a gate electrode. Adesirable resistivity of the W film is 20 μΩcm or lower. The resistivityof the W film can be reduced by increasing the crystal grain size but,if there are too many impurity elements such as oxygen in the W film,crystallization is inhibited to raise the resistivity. Accordingly, whenthe W film is formed by sputtering, a W target with a purity of 99.9 to99.9999% is used and a great care is taken not to allow impurities ingas phase to mix in the W film that is being formed. As a result, the Wfilm can have a resistivity of 9 to 20 μΩcm.

Sputtering can also be used to form a Ta film for the heat-resistantconductive layer 907. The Ta film is formed by using Ar as sputteringgas. If an appropriate amount of Xe or Kr is added to the sputteringgas, the internal stress of the obtained Ta film is eased to prevent theTa film from peeling off. The resistivity of a Ta film in α phase isabout 20 μΩcm and is usable as a gate electrode. On the other hand, theresistivity of a Ta film in β phase is about 180 μΩcm and is notsuitable for a gate electrode. A Ta film in α phase can readily beobtained by forming, as a base of a Ta film, a TaN film that has acrystal structure approximate to that of the α phase. Though not shownin the drawings, it is effective to form a silicon film doped withphosphorus (P) to a thickness of about 2 to 20 nm under theheat-resistant conductive layer 907. This improves adherence to theconductive film to be formed thereon and prevents oxidization. At thesame time, the silicon film prevents a minute amount of alkaline metalelement contained in the heat-resistant conductive layer 907 and 908from diffusing into the first shape gate insulating film 906. Whatevermaterial is used, a preferable resistivity range for the heat-resistantconductive layer 907 is 10 to 50 μΩcm.

In this embodiment, a TaN film is used for the first conductive film 907and a W film is used for the second conductive film 908 (FIG. 3A).

Next, resist masks 909 are formed using the photolithography technique.Then first etching treatment is carried out. The first etching treatmentis conducted under first etching conditions and second etchingconditions.

In this embodiment, an ICP etching apparatus is used, Cl₂, CF₄, and O₂are used as etching gas, the ratio of gas flow rate thereof is set to25/25/10, and RF (13.56 MHz) power of 3.2 W/cm² is given at a pressureof 1 Pa to generate plasma. RF (13.56 MHz) power of 224 mW/cm² is alsogiven to the substrate side (sample stage) so that substantiallynegative self-bias voltage is applied thereto. The W film is etchedunder the first etching conditions. The first etching conditions arethen switched to the second etching conditions without removing theresist masks. Under the second etching conditions, CF₄ and Cl₂ are usedas etching gas, the ratio of gas flow rate thereof is set to 30/30 SCCM,and RF (13.56 MHz) power is given at a pressure of 1 Pa to generateplasma. RF (13.56 MHz) power of 20 W is also given to the substrate side(sample stage) so that substantially negative self-bias voltage can beapplied.

Conductive films 910 to 913 having a first taper shape are formedthrough the first etching treatment. The angle of the tapered portionsof the conductive layers 910 to 913 is set to 15 to 30°. In order toetch the films without leaving any residue, the etching time isprolonged by about 10 to 20% for over-etching. The selective ratio ofthe silicon oxynitride film (the gate insulating film 906) to the W filmis 2 to 4 (typically, 3), and hence the exposed surface of the siliconoxynitride film is etched by about 20 to 50 nm through the over-etchingtreatment (FIG. 3B).

Then first doping treatment is performed to dope the semiconductorlayers with an impurity element of one conductivity type. An impurityelement for giving the n type conductivity is used in this doping stepwithout removing the resist masks 909. The semiconductor layers 902 to905 are partially doped with the impurity element using the first tapershape conductive layers 910 and 913 as masks, whereby first n typeimpurity regions 914 to 917 are formed in a self-aligning manner. Usedas the impurity element for imparting the n type conductivity is a Group15 element in the periodic table, typically phosphorus (P) or arsenic(As). The doping here uses phosphorus and ion doping. The concentrationof the impurity element for imparting the n type conductivity is 1×10²⁰to 1×10²¹ atoms/cm³ in the first n type impurity regions 914 to 917(FIG. 3B).

Second etching treatment is then conducted without removing the resistmasks. The second etching treatment is carried out under third etchingconditions and fourth etching conditions. In the second etchingtreatment, similar to the first etching treatment, the ICP apparatus isemployed, CF₄ and Cl₂ are used as etching gas, the ratio of flow ratethereof is set to 30/30 SCCM, and RF (13.56 MHz) power is given at apressure of 1 Pa to generate plasma. RF (13.56 MHz) power of 20 W isalso given to the substrate side (sample stage) so that a substantiallynegative self-bias voltage is applied thereto. Formed under the thirdetching conditions are conductive films 918 to 921 where the W film andthe TaN film are etched to the same degree (FIG. 3C).

While leaving the resist masks in their places, the etching conditionsare changed to the fourth etching conditions. Under the fourth etchingconditions, a mixture of CF₄, Cl₂, and O₂ is used as etching gas, and RF(13.56 MHz) power is given at a pressure of 1 Pa to generate plasma. RF(13.56 MHz) power of 20 W is also given to the substrate side (samplestage) so that substantially negative self-bias voltage is appliedthereto. The W film is etched under the fourth etching conditions toform second shape conductive films 922 to 925 (FIG. 3D).

Then second doping step is carried out (in which the semiconductorlayers are doped with an n type impurity element through the secondshape first conductive films 922 a to 925 a). As a result, second n typeimpurity regions 926 to 929 are respectively formed on the side of thechannel formation regions that are in contact with the first n typeimpurity regions 914 to 917. The concentration of the impurity in eachsecond n type impurity region is set to 1×10¹⁶ to 1×10¹⁹ atoms/cm³. Inthe second doping step, the semiconductor layers are doped with the ntype impurity element also through the tapered portions of the firstlayer second shape conductive films 922 a to 925 a. In thisspecification, portions of the second n type impurity regions thatoverlap the first layer second shape conductive films 922 a to 925 a arecalled Lov (‘ov’ stands for ‘overlap’) regions whereas portions of thesecond n type impurity regions that do not overlap the first layersecond shape conductive films 922 a to 925 a are called Loff (‘off’stands for ‘offset’) regions (FIG. 4A).

As shown in FIG. 4B, impurity regions 932 (932 a and 932 b) and 933 (933a and 933 b) are formed in the semiconductor layers 902 and 905,respectively, which are to serve as active layers of p-channel TFTs. Theconductivity type of the impurity regions 932 and 933 is reverse to theone conductivity type. The impurity regions 932 and 933 too are formedin a self-aligning manner by doping the semiconductor layers with animpurity element that gives the p type conductivity while using thesecond conductive layers 922 and 925 as masks. Prior to this doping,resist masks 930 and 931 are formed to cover the entire surfaces of thesemiconductor layers 903 and 904 that are to serve as active layers ofn-channel TFTs. The p type impurity regions 932 and 933 are formed byion doping using diborane (B₂H₆). The concentration of the impurity forimparting the p type conductivity is set to 2×10²⁰ to 2×10²¹ atoms/cm³in each of the p type impurity regions 932 and 933.

At a closer look, the p type impurity regions 932 and 933 contain theimpurity element that gives the n type conductivity. However, the p typeimpurity regions 932 and 933 have no problem in functioning as a sourceregion and a drain region of p-channel TFTs if they are doped with theimpurity element for imparting the p type conductivity in aconcentration 1.5 to 3 times higher than the concentration of theimpurity element that gives the n type conductivity.

Thereafter, a first interlayer insulating film 934 is formed on thesecond shape conductive layers 922 to 925 and the gate insulating film906 as shown in FIG. 4C. The first interlayer insulating film 934 is asilicon oxide film, a silicon oxynitride film, or a silicon nitridefilm, or a laminate having the above films in combination. In any case,the first interlayer insulating film 934 is formed from an inorganicinsulating material. The thickness of the first interlayer insulatingfilm 934 is set to 100 to 200 nm. If a silicon oxide film is used forthe first interlayer insulating film 934, the film is formed by plasmaCVD in which TEOS and O₂ are mixed, the reaction pressure is set to 40Pa, the substrate temperature is set to 300 to 400° C., and the highfrequency (13.56 MHz) power density is set to 0.5 to 0.8 W/cm² forelectric discharge. If a silicon oxynitride film is used for the firstinterlayer insulating film 934, the film may be formed by plasma CVDfrom SiH₄, N₂O, and NH₃, or from SiH₄ and N₂O. The film formationconditions in this case include setting the reaction pressure to 20 to200 Pa, the substrate temperature to 300 to 400° C., and the highfrequency (60 MHz) power density to 0.1 to 1.0 W/cm². The firstinterlayer insulating film 934 may be a silicon oxynitride hydrate filmformed from SiH₄, N₂O, and H₂. A silicon nitride film as the firstinterlayer insulating film can be formed similarly by plasma CVD fromSiH₄ and NH₃.

Then an activation step is conducted to activate the impurity elementsthat are used to dope the semiconductor layers in differentconcentrations and give them the n type or p type conductivity. Theactivation step is achieved by thermal annealing using an annealingfurnace. Laser annealing or rapid thermal annealing (RTA) may beemployed instead. Thermal annealing is conducted in a nitrogenatmosphere with the oxygen concentration being 1 ppm or less, preferably0.1 ppm or less, at a temperature of 400 to 700° C., typically 500 to600° C., and heat treatment in this embodiment is conducted at 550° C.for four hours. If a plastic substrate that has low heat-resistance isused as the substrate 900, laser annealing is preferred.

In this heat treatment step, the catalytic element (nickel) used in thestep of crystallizing the semiconductor layers is moved (gettered) tothe first n type impurity regions heavily doped with a Group 15 elementin the periodic table that has a gettering effect (phosphorus is used inthis embodiment). As the result of gettering, the concentration of thecatalytic element is reduced in the channel formation regions.

The activation step is followed by a step of hydrogenating thesemiconductor layers through heat treatment at 300 to 450° C. for 1 to12 hours while changing the atmosphere gas to an atmosphere containing 3to 100% hydrogen. This step is for terminating 10¹⁶ to 10¹⁸/cm³ of thesemiconductor layers by thermally excited hydrogen. Other usablehydrogenating methods include plasma hydrogenation (using hydrogenexcited by plasma). Whichever method is used, the defect density of thesemiconductor layers 902 to 905 is desirably reduced to 10¹⁶/cm³ orlower. To achieve this, the semiconductor layers are doped with 0.01 to0.1 atomic % hydrogen.

A second interlayer insulating film 935 is formed to an averagethickness of 1.0 to 2.0 μm from an organic insulating material. Thesecond interlayer insulating film may be formed of an organic resinmaterial such as polyimide, acrylic, polyamide, polyimideamide, or BCB(benzocyclobutene). For instance, when polyimide of the type that isthermally polymerized after applied to a substrate is used, the film isformed by baking in a clean oven at 300° C. If the second interlayerinsulating film is formed of acrylic, two-pack type is employed. Themain material is mixed with the curing agent, the mixture is applied tothe entire surface of the substrate using a spinner, the substrate ispre-heated on a holt plate at 80° C. for 60 seconds, and then thesubstrate is baked in a clean oven at 250° C. for 60 minutes to form thefilm.

Being formed of an organic insulating material, the second interlayerinsulating film 935 is capable of leveling the surface properly.Moreover, the interlayer insulating film can reduce parasiticcapacitance since organic resin materials are low in dielectric constantin general. However, organic resin materials are hygroscopic and are notsuitable as a protective film. Therefore, as in this embodiment, thesecond interlayer insulating film is used in combination with the firstinterlayer insulating film 934 that is formed from a silicon oxide film,a silicon oxynitride film, or a silicon nitride film.

The second interlayer insulating film 935 formed from an organicinsulating material may release moisture and gas. Light emittingelements are known to be easily degraded by moisture or gas (oxygen). Infact, in a light emitting device that uses an organic resin insulatingfilm to form an interlayer insulating film, it is conceivable that itslight emitting element is easily degraded by moisture and oxygenreleased from the organic resin insulating film due to heat generatedduring the light emitting device is in operation. Therefore, a firstinsulating film 936 is formed on the second interlayer insulating film935 that is formed from an organic insulating material.

A silicon oxide film, a silicon oxynitride film, a silicon nitride film,or the like is used for the first insulating film 936. The firstinsulating film 936 is formed here by sputtering or plasma CVD. Thefirst insulating film 936 may be formed after contact holes are formed.

A resist mask having a given pattern is then formed to form contactholes reaching the impurity regions that are formed in the semiconductorlayers to serve as source regions or drain regions. The contact holesare formed by dry etching. In this case, a mixture of CF₄ and O₂ is usedas etching gas to etch the first insulating film 936 first. The etchinggas is then changed to a mixture of CF₄, O₂, and He to etch the secondinterlayer insulating film 935 that is formed from an organic resinmaterial. Then the etching gas is switched back to CF₄ and O₂ to etchthe first interlayer insulating film 934. The etching gas is furtherchanged to CHF₃ in order to enhance the selective ratio with thesemiconductor layers, and the gate insulating film 906 is etched. Thecontact holes are thus obtained.

A metal conductive film is formed by sputtering or vacuum evaporationand patterned using a mask. The film is then etched to form wiring lines937 to 943. Though not shown in the drawings, the wiring lines in thisembodiment are formed from a laminate of a Ti film with a thickness of50 nm and an alloy film (Al—Ti alloy film) with a thickness of 500 nm.

A transparent conductive film is formed thereon to a thickness of 80 to120 nm. The film is then etched to form an anode 944 (FIG. 5A). Thetransparent conductive film used in this embodiment is an indium tinoxide (ITO) film or a film obtained by mixing 2 to 20% of zinc oxide(ZnO) with indium oxide.

The anode 944 is formed to come in contact and overlap with the drainwiring line 943, whereby the anode is electrically connected to thedrain region of the current controlling TFT (FIG. 5A). The anode 944 atthis point may receive heat treatment at 180 to 350° C.

Next, a third interlayer insulating film 945 is formed on the anode 944as shown in FIG. 5B. At this point, the substrate may be moved to aprocessing room (clean room) for forming a light emitting element. Inorder to avoid contamination or breakage of the TFT substrate by dustsin the air, a very thin film 946 having an anti-electrostatic effect(hereinafter referred to as anti-electrostatic film) is formed on thethird interlayer insulating film 945. The anti-electrostatic film 946 isformed from a material that can be removed by water washing (FIG. 5C).Instead of forming an anti-electrostatic film, the substrate may bestored in an anti-electrostatic carry case. Before changing processingrooms, the TFT substrate that has finished the steps above may besubjected to operation testing.

When the TFT substrate is brought into the processing room (clean room)for forming a light emitting element, the anti-electrostatic film 946 isremoved by water washing. Then the third interlayer insulating film 945is etched to form a bank 947 having an opening at a position thatcoincides with the pixel (light emitting element). A resist is used toform the bank 947 in this embodiment. The bank 947 in this embodiment isabout 1 μm in thickness, and a region of the bank 947 that covers theportion where the anode is in contact with the wiring line is tapered(FIG. 6A). The TFT substrate may be subjected to the operation testingagain after it is brought into the processing room for forming a lightemitting element.

Although a resist film is used for the bank 947 in this embodiment, apolyimide film, a polyamide film, an acrylic film, a BCB(benzocyclobutene) film, a silicon oxide film, or the like may be usedin some cases. The bank 947 may be inorganic or organic as long as it iscapable of insulating. If photosensitive acrylic is used to form thebank 947, it is preferable to etch a photosensitive acrylic film andthen perform heat treatment at 180 to 350° C. When a non-photosensitiveacrylic film is used, it is preferable to perform heat treatment at 180to 350° C. first and then etch to form the bank.

Next, wiping treatment is performed on the surface of the anode. In thisembodiment, the surface of the anode 944 is wiped using Bellclean (aproduct of Ozu Corporation) to level the surface of the anode 944 andremove dusts therefrom. In wiping, pure water is used as a washingliquid, the number of rotation of the axis around which Bellclean iswound is set to 100 to 300 rpm, and the depression value is set to 0.1to 1.0 mm (FIG. 6A).

Next, the TFT substrate is baked in a vacuum. In order to releasemoisture and gas from the resin insulating film for forming the bank,the vacuum exhaust is conducted at a constant degree of vacuum, forexample 0.01 Torr or less. The baking in a vacuum may be conducted afterremoving the anti-electrostatic film, after wiping treatment, or beforeforming light emitting element.

A second insulating film 948 is formed to cover the bank 947 and theanode 944. The second insulating film 948 is an organic resin film, suchas a polyimide film, a polyamide film, or a polyimideamide film, formedby spin coating, evaporation, sputtering, or the like to a thickness of1 to 5 nm. By forming this insulating film, cracking in the surface ofthe anode 944 can be avoided and degradation of the light emittingelement can be prevented.

An organic compound layer 949 and a cathode 950 are formed on the secondinsulating film 948 by evaporation. A MgAg electrode is used for thecathode of the light emitting element in this embodiment, but otherknown materials may be used instead. The organic compound layer 949 is alaminate that has, in addition to a light emitting layer, a holeinjection layer, a hole transporting layer, an electron transportinglayer, an electron injection layer, a buffer layer, etc. in combination.The structure of the organic compound layer used in this embodiment willbe described in detail below.

In this embodiment, copper phthalocyanine is used for a hole injectionlayer whereas α-NPD is used for a hole transporting layer. Both of thelayers are formed by evaporation.

A light emitting layer is formed next. In this embodiment, differentmaterials are used for different light emitting layers to obtain organiccompound layers that emit light of different colors. The organiccompound layers formed in this embodiment are three types: ones thatemit red light, ones that emit green light, and ones that emit bluelight. All types of organic compound layers are formed by evaporation.Therefore, it is possible to use a metal mask to form light emittinglayers from a material that varies between different pixels.

A light emitting layer that emits red light is formed from Alq₃ dopedwith DCM. Instead, N,N′-disalicylidene-1,6-hexanediaminate) zinc (II)(Zn(salhn)) doped with(1,10-phenanthroline)-tris(1,3-diphenyl-propane-1,3-dionato) europium(III) (Eu(DBM)₃(Phen)) that is an Eu complex may be used. Other knownmaterials may also be used.

A light emitting layer that emits green light can be formed from CBP andIr(ppy)₃ by coevaporation. It is preferable to form a hole blockinglayer from BCP in this case. An aluminum quinolilate complex (Alq₃) anda benzoquinolinolate beryllium complex (BeBq) may be used instead. Thelayer may be formed from a quinolilate aluminum complex (Alq₃) using asdopant Coumarin 6, quinacridon, or the like. Other known materials mayalso be used.

A light emitting layer that emits blue light can be formed from DPVBithat is a distylyl derivative, N,N′-disalicyliden-1,6-hexanediaminate)zinc (II) (Zn(salhn)) that is a zinc complex having an azomethinecompound as its ligand, or 4,4′-bis(2,2-diphenyl-vinyl)-biphenyl (DPVBi)doped with perylene. Other known materials may also be used.

An electron transporting layer is formed next. 1,3,4-oxadiazolederivatives, 1,2,4-triazole derivatives (e.g., TAZ), or the like can beused for the electron transporting layer. In this embodiment, a1,2,4-triazole derivative (TAZ) is formed by evaporation to a thicknessof 30 to 60 nm.

Through the above steps, the organic compound layer having a laminatestructure is completed. In this embodiment, the organic compound layer949 is 10 to 400 nm (typically 60 to 150 nm) in thickness, and thecathode 950 is 80 to 200 nm (typically 100 to 150 nm) in thickness.

After the organic compound layer is formed, the cathode 950 of the lightemitting element is formed by evaporation. In this embodiment, MgAg isused for a conductive film that constitutes the cathode of the lightemitting element. However, a Al—Li alloy film (an alloy film of aluminumand lithium) or a film obtained by co-evaporation of aluminum and anelement belonging to Group 1 or 2 in the periodic table may also beused.

Thus completed is a light emitting device having the structure shown inFIG. 6B. A portion 951 where the anode 944, the organic compound layer949, and the cathode 950 overlap corresponds to the light emittingelement.

A p-channel TFT 1000 and an n-channel TFT 1001 are TFTs of the drivingcircuit, and constitute a CMOS. A switching TFT 1002 and a currentcontrolling TFT 1003 are TFTs of the pixel portion. The TFTs of thedriving circuit and the TFTs of the pixel portion can be formed on thesame substrate.

In the case of a light emitting device using a light emitting element,its driving circuit can be operated by a power supply having a voltageof about 5 to 6V, 10 V, at most. Therefore degradation of TFTs due tohot electron is not a serious problem.

Embodiment 2

This embodiment describes another example of process of manufacturing alight emitting device with reference to FIGS. 19 to 22B.

Following the description in Embodiment 1, the steps up through the stepof forming two layers of conductive films 907 and 908 on the gateinsulating film 906 as shown in FIG. 3A are finished.

Subsequently, a process where the conductive films 907 and 908 areetched using masks 909 a to 909 d to form conductive layers 3901 to 3904having a first taper shape is described in FIG. 20A. ICP (inductivelycoupled plasma) etching is used for this etching. Though etching gas isnot limited, CF₄, Cl₂, and O₂ are used to etch a W film and a tantalumnitride film. The gas flow rate of CF₄, Cl₂, and O₂ is respectively setto 25/25/10, and RF (13.56 MHz) power of 500 W is given to a coiledelectrode at a pressure of 1 Pa for the etching. RF (13.56 MHz) power of150 W is also given to the substrate side (sample stage) so thatsubstantially negative self-bias voltage can be applied. Under thesefirst etching conditions, mainly the W film is etched to have a givenshape.

Thereafter, the etching gas is changed to CF₄ and Cl₂, the ratio of gasflow rate thereof is set to 30/30, and RF (13.56 MHz) power of 500 W isgiven to a coiled electrode at a pressure of 1 Pa to generate plasma for30 second etching. RF (13.56 MHz) power of 20 W is also given to thesubstrate side (sample stage) so that substantially negative self-biasvoltage can be applied. With the mixture of CF₄ and Cl₂, the tantalumnitride film and the W film are etched at about the same rate. Thusformed are the conductive layers 3901 to 3904 having a first tapershape. The taper thereof has an angle of 45 to 75°. In order to etch thefilms without leaving any residue on the second insulating film, theetching time is prolonged by about 10 to 20% for over-etching. Surfacesof regions of the gate insulating film 906 that are not covered with thefirst taper shape conductive layers 3901 to 3904 are etched and thinnedby about 20 to 50 nm (FIG. 20A).

Subsequently, second etching treatment is conducted as shown in FIG. 20Bwithout removing the masks 909 a to 909 d. In the second etchingtreatment, CF₄, CL₂, and O₂ are mixed as etching gas, the ratio of gasflow rate thereof is set to 20/20/20, and an RF (13.56 MHz) power of 500W is given to a coiled electrode at a pressure of 1 Pa to generateplasma. The substrate side (sample stage) receives an RF (13.56 MHz)power of 20 W to apply a self-bias voltage lower than that in the firstetching treatment. Under these etching conditions, the W film that isthe second conductive film is etched. Thus formed are conductive layers3905 to 3908 having a second taper shape. Surfaces of regions of thegate insulating film 906 that are not covered with the second tapershape conductive layers 3905 to 3908 are etched and thinned by about 20to 50 nm.

After removing the resist masks, first doping treatment is conducted todope the semiconductor layers with an impurity element that gives the ntype conductivity (n type impurity element). The first doping treatmentuses ion doping for injecting ions without mass separation. In thedoping, the second taper shape conductive layers 3905 to 3908 are usedas masks and phosphine (PH₃) gas diluted by hydrogen or phosphine gasdiluted by rare gas is used to form n type impurity regions 3909 to 3912that contain an n type impurity element in a first concentration in thesemiconductor layers 902 to 905. The n type impurity regions 3909 to3912 formed through this doping, which contain an n type impurityelement in a first concentration, contain phosphorus in a concentrationof 1×10¹⁶ to 1×10¹⁷ atoms/cm³ (FIG. 20C).

Formed next are first masks 3913 and 3915 that completely cover thesemiconductor layers 902 and 905, respectively, and a second mask 3914that covers the second taper shape conductive layer 3907 on thesemiconductor layer 904 and covers a part of the semiconductor layer904. Then, second doping treatment is conducted. In the second dopingtreatment, the semiconductor layer 903 is doped through the second tapershape conductive layer 3906 a to have an n type impurity region 3917that contains an n type impurity element in a second concentration and ntype impurity regions 3916 and 3918 that contain an n type impurityelement in a third concentration each. The n type impurity region 3917formed through this doping, which contains an n type impurity element ina second concentration, contain phosphorus in a concentration of 1×10¹⁷to 1×10¹⁹ atoms/cm³. The n type impurity regions 3916 and 3918 formedthrough this doping, which contain an n type impurity element in a thirdconcentration each, contain phosphorus in a concentration of 1×10²⁰ to1×10²¹ atoms/cm³ (FIG. 20D).

As described above, the n type impurity region that contains an n typeimpurity element in a second concentration and the n type impurityregions that contain an n type impurity element in a third concentrationeach are formed in one doping step in this embodiment. However, thedoping step may be divided into two steps to dope the semiconductorlayer with the impurity element.

Next, masks 3919 and 3920 for covering the semiconductor layers 903 and904 are formed as shown in FIG. 21A to conduct third doping treatment.In the doping, diborane (B₂H₆) gas diluted by hydrogen or diborane gasdiluted by rare gas is used to form, in the semiconductor layers 902 and905, p type impurity regions 3921 and 3923 that contain a p typeimpurity element in a first concentration and p type impurity regions3922 and 3924 that contain a p type impurity element in a secondconcentration. The p type impurity regions 3921 and 3923, which containa p type impurity element in a first concentration, contain boron in aconcentration of 2×10²⁰ to 3×10²¹ atoms/cm³ each. The p type impurityregions 3922 and 3924, which contain a p type impurity element in asecond concentration, contain boron in a concentration of 1×10¹⁸ to1×10²⁰ atoms/cm³ each. The p type impurity regions 3922 and 3924 thatcontain a p type impurity element in a second concentration are formedin regions that overlap the second taper shape conductive layers 3905 aand 3908 a.

As shown in FIG. 21B, a first interlayer insulating film 3925 is formedfrom a silicon nitride film or a silicon oxynitride film formed byplasma CVD to have a thickness of 50 nm. In order to give activationtreatment to the impurity elements that are used to dope thesemiconductor layers, heat treatment is conducted at 410° C. using afurnace. This heat treatment also hydrogenates the semiconductor layersby hydrogen released from the silicon nitride film or silicon oxynitridefilm.

The heat treatment may be achieved by other methods than the method thatuses a furnace. A heat treatment method by RTA may be used instead(including an RTA method using gas or light as the heat source). If theheat treatment is carried out using a furnace, an insulating film forcovering the gate electrode and the gate insulating film is formed priorto heat treatment, or the heat treatment atmosphere is set to a reducedpressure nitrogen atmosphere, in order to prevent oxidization of theconductive film that forms the gate electrode. Alternatively, thesemiconductor layers may be irradiated with second harmonic (532 nm)light of a YAG laser. As can be seen in the above, there are severalways to activate the impurity elements used to dope the semiconductorlayers, and an operator can choose from them one that suits him.

On the first interlayer insulating film 3925, a second interlayerinsulating film 3926 is formed from acrylic. A silicon nitride film isformed on the second interlayer insulating film 3926 by sputtering as afirst insulating film 3927 for protecting the TFTs from impurities(hereinafter the film is also called a barrier insulating film) (FIG.21C).

On the barrier insulating film 3927, a transparent conductive film isformed to have a thickness of 80 to 120 nm and is etched to form ananode 3928 (FIG. 22A). The transparent electrode in this embodiment isan indium tin oxide (ITO) film, or a transparent conductive filmobtained by mixing indium oxide with 2 to 20% of zinc oxide (ZnO).

A resist mask having a given pattern is then formed to form contactholes reaching respectively the impurity regions 3916, 3918, 3921, and3923 that are formed in the semiconductor layers to serve as sourceregions or drain regions. The contact holes are formed by dry etching.

A metal conductive film is formed by sputtering or vacuum evaporationand patterned using a mask. The film is then etched to form wiring lines3929 to 3935. Though not shown in the drawings, the wiring lines in thisembodiment are formed from a laminate of a Ti film with a thickness of50 nm and an alloy film (Al—Ti alloy film) with a thickness of 500 nm.

Next, a third interlayer insulating film 3936 is formed to cover theanode 3928 and the wiring lines 3929 to 3935. Now, the manufactureprocess proceeds to a step where the substrate is moved from aprocessing room for forming a TFT substrate (hereinafter referred to asfirst clean room) to a processing room for forming a light emittingelement (hereinafter referred to as second clean room) in order toreduce the risk of mixing the alkaline metal from the alkaline metalmaterial, such as Al or Mg, used for the cathode of the light emittingelement into the active layers of the TFTs.

To avoid contamination of the TFT substrate by dusts in the air andelectrostatic discharge damage of the TFT substrate by staticelectricity during the moving, a very thin film 3937 having ananti-electrostatic effect (hereinafter referred to as anti-electrostaticfilm) is formed on the third interlayer insulating film 3936. Theanti-electrostatic film 3937 is formed from a material that can beremoved by water washing or like other simple methods (FIG. 22A).Instead of forming an anti-electrostatic film, the substrate may bestored in a case capable of preventing electrostatic discharge damageduring moving. Before changing processing rooms, the TFT substrate thathas finished the steps above may be subjected to operation testing. Thesteps up through this point are for processing in the first processingroom (clean room) which is shown in the flow chart of FIG. 19.

Various cases are conceivable in moving the TFT substrate from the firstprocessing room to the second processing room. For example, the TFTsubstrate may be moved between different buildings on the same premise,or between factories (processing rooms, e.g., clean rooms) located indifferent sites but owned by the same incorporation, or betweenfactories (processing rooms, e.g., clean rooms) owned by differentincorporations. In any case, moving is carried out while taking a carenot to damage the TFT substrate.

Then, the manufacture process proceeds to processing in the secondprocessing room (clean room) which is shown in a flow chart of FIG. 19.The TFT substrate brought into the second processing room (clean room)is washed with water to remove the anti-electrostatic film 3937. Thirdinterlayer insulating film 3936 is etched to form a bank 3938. The bankhas an opening at a position that coincides with the pixel (lightemitting element), and is tapered to cover a portion where the wiringline 3934 is in contact with the anode 3928 and to cover the edges ofthe anode 3928. In this embodiment, the bank 3938 is formed from aresist to have a thickness of about 1 μm. At this point, the operationtesting may be performed again on the TFT substrate brought into thesecond processing room.

In order to prevent degradation of the light emitting element due tomoisture and gas released from the bank 3938, the surface of the bank3938 is covered with a second insulating film 3939 that is a siliconnitride film or the like. The second insulating film 3939 is aninsulating film for protecting the light emitting element from moistureand gas, which cause degradation of the light emitting element.Accordingly, the second insulating film 3939 is also called a secondbarrier insulating film 3939.

Next, the TFT substrate is baked in a vacuum. In order to releasemoisture and gas from the resin insulating film for forming the bank,the vacuum exhaust is conducted at a constant degree of vacuum, forexample 0.01 Torr or less. The baking in a vacuum may be conducted afterremoving the anti-electrostatic film, or before forming light emittingelement.

Next, an organic compound layer 3940 is formed by evaporation on thesecond insulating film 3939 such that the organic compound layer comesinto contact with the anode 3928. On the organic compound layer 3940, acathode 3941 is formed by evaporation. This embodiment uses a MgAgelectrode for the cathode of the light emitting element, but other knownmaterials may be used instead. The organic compound layer 3940 is alaminate that has, in addition to a light emitting layer, a holeinjection layer, a hole transporting layer, an electron transportinglayer, an electron injection layer, a buffer layer, etc. in combination.The organic compound layer in this embodiment is formed by following thedescription of Embodiment 1.

Thus completed is a light emitting device having the structure shown inFIG. 22B. A portion 3942 where the anode 3928, the organic compoundlayer 3940, and the cathode 3941 overlap corresponds to the lightemitting element.

As described above, by separating a processing room for forming a TFTsubstrate (e.g., a first clean room) from a processing room for forminga light emitting element (e.g., a second clean room), an active layer ofa TFT can be protected from an alkaline metal material such as Al or Mgused for a cathode of a light emitting element and an excellent lightemitting device is obtained.

Embodiment 3

Following the description of Embodiment 1 or 2, the manufacture processup through the step of forming the second interlayer insulating film(935 or 3926) is finished. Then, instead of forming the first insulatingfilm 936 of Embodiment 1, plasma treatment is performed on the secondinterlayer insulating film to modify the surface of the secondinterlayer insulating film (935 or 3926). This method will be describedwith reference to FIG. 7.

The second interlayer insulating film (935 or 3926) receives plasmatreatment in, for example, one or more kinds of gas selected from thegroup consisting of hydrogen, nitrogen, hydrocarbon, halogenated carbon,hydrogen fluoride, and rare gas (such as Ar, He, or Ne), so that a coatis newly formed on the surface of the second interlayer insulating film(935 or 3926) or the existing functional group on the surface is changedto a different functional group. The surface modification of the secondinterlayer insulating film (935 or 3926) is thus achieved. As shown inFIG. 7, a dense film 935B is formed on the surface of the secondinterlayer insulating film (935 or 3926). This film is called a curedfilm 935B in this specification. The film prevents release of gas ormoisture from the organic resin film.

In this embodiment, an anode (ITO) is formed after the surfacemodification, thereby avoiding a situation in which materials havingdifferent thermal expansion coefficients receive heat treatment whilebeing in direct contact with each other. Therefore, cracking in the ITOelectrode is prevented and degradation of the light emitting element canbe prevented. The plasma treatment for the second interlayer insulatingfilm (935 or 3926) may be given before or after forming contact holes.

The cured film 935B is formed by performing plasma treatment on thesurface of the second interlayer insulating film (935 or 3926) that isformed of an organic insulating material in one or more kinds of gasselected from the group consisting of hydrogen, nitrogen, hydrocarbon,halogenated carbon, hydrogen fluoride, and rare gas (such as Ar, He, orNe). Accordingly, the cured film 935B contains one of the gas elementsout of hydrogen, nitrogen, hydrocarbon, halogenated carbon, hydrogenfluoride, and rare gas (such as Ar, He, or Ne).

Embodiment 4

Following the description of Embodiment 1 or 2, the manufacture processup through the step of forming the second interlayer insulating film(935 or 3926) is finished. Then, as shown in FIG. 12, a DLC film 936B asthe first insulating film 936 is formed on the second interlayerinsulating film (935 or 3926).

A characteristic of the DLC film is having a Raman spectrum distributionthat has an asymmetric peak around 1550 cm⁻¹ and a shoulder around 1300cm⁻¹. When measured by a microhardness tester, the DLC film exhibits ahardness of 15 to 25 GPa. The DLC film is also characterized by itsexcellent resistance to chemicals. Moreover, the DLC film can be formedat a temperature range between room temperature and 100° C. Examples ofthe method that can be used to form the DLC film include sputtering, ECRplasma CVD, high frequency plasma CVD, and ion beam evaporation. Thethickness of the DLC film is set to 5 to 50 nm.

Embodiment 5

This embodiment describes a case of employing other insulating filmsthan a DLC film to form as the insulating film 936 on the secondinterlayer insulating film (935, 3926).

Following the description of Embodiment 1 or 2, the manufacture processup through the step of forming the second interlayer insulating film(935 or 3926) is finished. Then, as the first insulating film 936, asilicon nitride film 936 is formed by sputtering using silicon as atarget. The film formation conditions can be set suitably, but it isparticularly preferable to use nitrogen (N₂) or mixture of nitrogen andargon as sputtering gas and apply a high frequency power for sputtering.The substrate temperature is set to room temperature and it is notalways necessary to use heating means. If an organic insulating film isused as the interlayer insulating film, it is preferred to form thesilicon nitride film without heating the substrate. In order to removethe adsorbed or occluded moisture well, dehydrogenating treatment ispreferably conducted by heating the substrate in vacuum at 50 to 100° C.for several minutes to several hours. To give an example of the filmformation conditions, a 1 to 2 Ωsq. silicon target doped with boron isused, nitrogen gas alone is supplied, a high frequency power (13.56 MHz)of 800 W is given at 0.4 Pa, and the size of the target is set to 152.4mm in diameter. The film formation rate obtained under these conditionsis 2 to 4 nm/min.

The thus obtained silicon nitride film contains impurity elements suchas oxygen and hydrogen in a concentration of 1 atomic % or less, and has80% or higher transmissivity in the visible light range. Thetransparency of this film is proved to be high especially by the factthat the film has a transmissivity of 80% or above at a wavelength of400 nm. Furthermore, this method is capable of forming a dense filmwithout seriously damaging the surface.

As described above, a silicon nitride film can be used for theinsulating film 936. The subsequent steps are identical with those inEmbodiment 1 or 2.

Embodiment 6

This embodiment describes a case of employing other insulating filmsthan a DLC film to form as the first insulating film 936 on the secondinterlayer insulating film (935, 3926).

Following the description of Embodiment 1 or 2, the manufacture processup through the step of forming the second interlayer insulating film(935 or 3926) is finished. Then, an Al_(X)N_(Y) film is formed using analuminum nitride (AlN) target under an atmosphere obtained by mixingargon gas and nitrogen gas. The acceptable range for the concentrationof impurities, oxygen, in particular, contained in the Al_(X)N_(Y) filmis less than 0 to 10 atomic %. The oxygen concentration can becontrolled by adjusting sputtering conditions (the substratetemperature, the type of raw material gas used, the flow rate thereof,the film formation pressure, etc.) appropriately. Alternatively, thefilm may be formed using an aluminum (Al) target under an atmospherecontaining nitrogen gas. The film may be formed by evaporation or otherknown techniques instead of sputtering.

Other than the Al_(X)N_(Y) film, it is possible to use a AlN_(X)O_(Y)film that is formed using an aluminum nitride (AlN) target under anatmosphere obtained by mixing argon gas, nitrogen gas, and oxygen gas.The acceptable range for concentration of nitrogen contained in theAlN_(X)O_(Y) film is a few atomic % or more, preferably 2.5 to 47.5atomic %. The nitrogen concentration can be controlled by adjustingsputtering conditions (the substrate temperature, the type of rawmaterial gas used, the flow rate thereof, the film formation pressure,etc.) appropriately. Alternatively, the film may be formed using analuminum (Al) target under an atmosphere containing nitrogen gas andoxygen gas. The film may be formed by evaporation or other knowntechniques instead of sputtering.

The above Al_(X)N_(Y) film and AlN_(X)O_(Y) film are both highlylight-transmissive (having a transmissivity of 80 to 91.3% in thevisible light range) and do not block light emitted from the lightemitting element.

As described in the above, a Al_(X)N_(Y) film or AlN_(X)O_(Y) film canbe used for the insulating film 936. The subsequent steps are identicalwith those in Embodiment 1.

Embodiment 7

Following the description of Embodiment 1 or 2, the manufacture processup through the step of forming the second interlayer insulating film(935 or 3926) is finished. Then, as shown in FIG. 13, the surface of thesecond interlayer insulating film is modified by plasma treatment toform a cured film 935B on the surface. A DLC film 936B is formed on thecured film 935B. Sputtering, ECR plasma CVD, high frequency plasma CVD,ion beam evaporation, etc. can be used to form the DLC film 936B to havea thickness of 5 to 50 nm.

Embodiment 8

The bank (947 or 3938) is formed in accordance with the manufactureprocess in Embodiment 1 or 2. Then, plasma treatment is performed on thesurface of the bank (947 or 3938) to modify the surface of the bank (947or 3938). This case will be described with reference to FIG. 8.

An organic resin insulating film is used to form the bank (947 or 3938).Undesirably, the organic resin insulating film is easy to releasemoisture or gas due to heat generated while the light emitting device isin operation.

Accordingly, after the heat treatment, plasma treatment is conducted forsurface modification of the bank as shown in FIG. 8. The plasmatreatment is carried out in one or more kinds of gas selected from thegroup consisting of hydrogen, nitrogen, halogenated carbon, hydrogenfluoride, and rare gas.

As a result, the surface of the bank becomes dense to form a cured filmthat contains one or more kinds of gas elements selected from the groupconsisting of hydrogen, nitrogen, halogenated carbon, hydrogen fluoride,and rare gas. The cured film can prevent release of moisture and gas(oxygen) from the inside, thereby preventing degradation of the lightemitting element.

This embodiment may be combined with any of Embodiments 1 through 7.

Embodiment 9

Following the description of Embodiment 1, the manufacture process upthrough the step of forming the second interlayer insulating film (935or 3926) is finished (FIG. 18A). Then, a first insulating film 936 isformed on the second interlayer insulating film (935 or 3926). The firstinsulating film 936 may be the DLC film, silicon nitride film, aluminumnitride film, or aluminum nitride oxide film described in Embodiment 2or 3. On the first insulating film 936, an ITO film is formed andpatterned into a desired shape to form an anode 1937.

A resist mask having a given pattern is then formed to form contactholes reaching the impurity regions that are formed in the semiconductorlayers to serve as source regions or drain regions. The contact holesare formed by dry etching or the like. This is done in accordance withEmbodiment 1.

A metal conductive film is formed by sputtering or vacuum evaporationand etched to form wiring lines 1938 to 1944. Similar to Embodiment 1,the wiring lines 1938 to 1944 are formed from a laminate of a Ti filmwith a thickness of 50 nm and an alloy film (Al—Ti alloy film) with athickness of 500 nm.

In the case where the anode 1937 is formed before forming the wiringlines 1938 to 1944 as in this embodiment (FIG. 18B), a problem such asbreaking of wire is not caused even when the anode is formed from amaterial of poor coverage because the broken wiring line 1943 issituated on the anode 1938.

After the wiring lines are formed, a bank, an organic compound layer,and a cathode are formed in accordance with Embodiment 1.

This embodiment may be combined with Embodiments 1 through 7.

Embodiment 10

This embodiment describes a method in which a semiconductor film toserve as an active layer of a TFT is crystallized using a catalyticelement and then the concentration of the catalytic element in theobtained crystalline semiconductor film is reduced.

In FIG. 17A, a substrate 1100 is preferably formed from bariumborosilicate glass, alumino borosilicate glass, or quartz. On thesurface of the substrate 1100, an inorganic insulating film with athickness of 10 to 200 nm is formed as a base insulating film 1101. Anexample of a suitable base insulating film is a silicon oxynitride filmformed by plasma CVD. A first silicon oxynitride film is formed to havea thickness of 50 nm from SiH₄, NH₃, and N₂O, and a second siliconoxynitride film is formed next to have a thickness of 100 nm from SiH₄and N₂O to obtain the base insulating film. The base insulating film1101 is provided to prevent an alkaline metal contained in the glasssubstrate from diffusing into the semiconductor film to be formed in theupper layer, and therefore may be omitted if a quartz substrate is used.

A silicon nitride film 1102 is formed on the base insulating film 1101.The silicon nitride film 1102 is provided to prevent the catalyticelement (typically, nickel) to be used later in a step of crystallizingthe semiconductor film from clinging to the base insulating film 1101,and to avoid the adverse effect of oxygen contained in the baseinsulating film 1101. Note that the silicon nitride film 1102 is formedby plasma CVD to have a thickness of 1 to 5 nm.

An amorphous semiconductor film 1103 is formed on the silicon nitridefilm 1102. A semiconductor material mainly containing silicon is usedfor the amorphous semiconductor film 1103. The amorphous semiconductorfilm is typically an amorphous silicon film or an amorphous silicongermanium film formed by plasma CVD, reduced pressure CVD, or sputteringto have a thickness of 10 to 100 nm. In order to obtain satisfactorycrystals, the concentration of impurities such as oxygen and nitrogencontained in the amorphous semiconductor film 1103 is reduced to 5×10¹⁸atoms/cm³ or lower. These impurities can hinder crystallization of theamorphous semiconductor film and, after crystallization, increase thedensity of trap center and recombination center. For that reason, it isdesirable to use a highly pure material gas and a ultra high vacuum CVDapparatus equipped with a mirror finish reaction chamber (processed byfield polishing) and with an oil-free vacuum exhaust system. The baseinsulating film 1101, the silicon nitride film 1102, and the amorphoussemiconductor film 1103 are continuously formed without exposing thesubstrate to the air.

The surface of the amorphous silicon film 1103 is doped with a metalelement having a catalytic function that accelerates crystallization(FIG. 17B). Examples of the metal element having a catalytic functionthat accelerates crystallization of a semiconductor film include iron(Fe), nickel (Ne), cobalt (Co), ruthenium (Ru), rhodium (Rh), palladium(Pd), osmium (Os), iridium (Ir), platinum (Pt), copper (Cu), and gold(Au). One or more kinds of metal elements selected from the above can beused. Typically, nickel is chosen and a nickel acetate solutioncontaining 1 to 100 ppm of nickel by weight is applied by a spinner toform a catalyst-containing layer 1104. To make sure the solution isapplied smoothly, surface treatment is performed on the amorphoussilicon film 1103. The surface treatment includes forming a very thinoxide film from an ozone-containing aqueous solution, etching the oxidefilm with a mixture of fluoric acid and a hydrogen peroxide aqueoussolution to form a clean surface, and again forming a very thin oxidefilm from the ozone-containing solution. Since a surface of asemiconductor film such as a silicon film is inherently hydrophobic, thenickel acetate solution can be applied evenly by forming an oxide filmin this way.

The method of forming the catalyst-containing layer 1104 is not limitedthereto, of course, and sputtering, evaporation, plasma treatment, orthe like may be used instead.

While keeping the amorphous silicon film 1103 in contact with thecatalyst-containing later 1104, heat treatment for crystallization iscarried out. Furnace annealing using an electric furnace, or rapidthermal annealing (RTA) using a halogen lamp, a metal halide lamp, axenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, a highpressure mercury lamp, etc. is employed for the heat treatment.

If RTA is chosen, a lamp light source for heating is lit for 1 to 60seconds, preferably 30 to 60 seconds, which is repeated 1 to 10 times,preferably 2 to 6 times. The intensity of light emitted from the lamplight source can be set arbitrarily, as long as the semiconductor filmis heated to reach 600 to 1000° C., preferably 650 to 750° C., in aninstant. When the temperature thereof reaches this high, thesemiconductor film alone is instantaneously heated but the substrate1100 is not deformed in itself. The amorphous semiconductor film is thuscrystallized to obtain a crystalline silicon film 1105 shown in FIG.17C. Crystallization by such treatment is achieved only when thecatalyst-containing layer is provided.

If furnace annealing is chosen instead, heat treatment at 500° C. isconducted for an hour to release hydrogen contained in the amorphoussilicon film 1103 prior to the heat treatment for crystallization. Then,the substrate receives heat treatment in an electric furnace in anitrogen atmosphere at 550 to 600° C., preferably at 580° C., for fourhours to crystallize the amorphous silicon film 1103. The crystallinesilicon film 1105 shown in FIG. 17C is thus formed.

It is effective to irradiate the crystalline silicon film 1105 withlaser light in order to raise the crystallization ratio (the ratio ofcrystal components to the entire volume of the film) and repair defectsremaining in crystal grains.

The thus obtained crystalline silicon film 1105 has a remainingcatalytic element (nickel, here) in a concentration higher than 1×10¹⁹atoms/cm³ in average. The remaining catalytic element can affect TFTcharacteristics, and therefore the concentration of the catalyticelement in the semiconductor film has to be reduced. How to reduce theconcentration of the catalytic element in the semiconductor filmsubsequent to the crystallization step is described.

First, a thin layer 1106 is formed on the surface of the crystallinesilicon film 1105 as shown in FIG. 17D. In this specification, the thinlayer 1106 formed on the crystalline silicon layer 1105 is called abarrier layer 1106, for the layer is provided to prevent the crystallinesilicon film 1105 from being etched when a gettering site is removedlater.

The thickness of the barrier layer 1106 is set to 1 to 10 nm. A simpleway to obtain the barrier layer is to form a chemical oxide by treatingthe surface with ozone water. A chemical oxide can be formed also whentreating with an aqueous solution in which hydrogen peroxide water ismixed with sulfuric acid, hydrochloric acid, or nitric acid. Otherusable methods include plasma treatment in an oxidization atmosphere,and oxidization treatment by ozone generated through UV irradiation inan atmosphere containing oxygen. Alternatively, a thin oxide film formedby heating in a clean oven until it reaches 200 to 350° C. may be usedas the barrier layer. An oxide film formed by plasma CVD, sputtering, orevaporation to have a thickness of 1 to 5 nm may also be used as thebarrier layer. In any case, the film used as the barrier layer has toallow the catalytic element to move into a gettering site in thegettering step, while being capable of preventing etchant from seepinginto the crystalline silicon film 1105 (protecting the film 1105 againstthe etchant) in the step of removing the gettering site. Examples ofsuch film include a chemical oxide film formed through ozone watertreatment, a silicon oxide (SiO_(X)) film, and a porous film.

On the barrier layer 1106, a second semiconductor film (typically, anamorphous silicon film) is formed as a gettering site 1107 to have athickness of 20 to 250 nm. The second semiconductor film contains a raregas element in a concentration of 1×10²⁰ atoms/cm³ or higher. Thegettering site 1107, which is to be removed later, is preferably a lowdensity film in order to increase the selective ratio to the crystallinesilicon film 1105 in etching.

A rare gas element itself is inert in a semiconductor film. Thereforethe rare gas element does not affect the crystalline silicon film 1105.One or more kinds of elements selected from the group consisting ofhelium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) areused as the rare gas element. The present invention is characterized inthat the rare gas elements are used as ion sources to form a getteringsite and that a semiconductor film containing these elements are formedto serve as the gettering site.

To make sure the gettering is conducted thoroughly, heat treatment isneeded at this point. The heat treatment is achieved by furnaceannealing or RTA. If furnace annealing is chosen, heat treatment isconducted in a nitrogen atmosphere at 450 to 600° C. for 0.5 to 12hours. If RTA is chosen, a lamp light source for heating is lit for 1 to60 seconds, preferably 30 to 60 seconds, which is repeated 1 to 10times, preferably 2 to 6 times. The intensity of light emitted from thelamp light source can be set arbitrarily, as long as the semiconductorfilm is heated to reach 600 to 1000° C., preferably 700 to 750° C., inan instant.

During gettering, the catalytic element in a to-be-gettered region (trapsite) is released by thermal energy and is moved to the gettering sitethrough diffusion. Accordingly, gettering is dependent on the processtemperature and gettering progresses in a shorter period of time at ahigher temperature. In the present invention, the distance the catalyticelement moves during gettering is about the same as the thickness of thesemiconductor film, and therefore gettering in the present invention iscompleted in a relatively short period of time (FIG. 17E).

This heat treatment does not crystallize the semiconductor film 1107that contains a rare gas element in a concentration of 1×10¹⁹ to 1×10²¹atoms/cm³, preferably 1×10²⁰ to 1×10²¹ atoms/cm³, more desirably 5×10²⁰atoms/cm³. This is supposedly because the rare gas element is notre-discharged in the above range of the process temperature and theremaining elements hinder crystallization of the semiconductor film.

After the gettering step is ended, the gettering site 1107 is removed byselective etching. The etching method employed may be dry etching byClF₃ without using plasma, or wet etching using hydrazine or an alkalinesolution such as an aqueous solution that contains tetraethyl ammoniumhydroxide (chemical formula: (CH₃)₄NOH). The barrier layer 1106functions as an etching stopper at this point. Thereafter, the barrierlayer 1106 is removed using fluoric acid.

In this way, a crystalline silicon film 1108 in which the concentrationof the catalytic element is reduced to 1×10¹⁷ atoms/cm³ or less isobtained as shown in FIG. 17F. The thus formed crystalline silicon film1108 is a mass of thin rod-like crystals, or thin flattened rod-likecrystals due to the effect of the catalytic element. Macroscopically,each of the crystals grows with a specific orientation.

This embodiment may be combined with Embodiments 1 through 9.

Embodiment 11

As this embodiment, the following will specifically describe a processin which the light emitting panel produced by a combined manufacturingstep of Embodiments 1 to 10 as illustrated in FIG. 6B is caused to becompleted as a light emitting device, referring to FIGS. 9A and 9B.

FIG. 9A is a top view of the light emitting panel wherein the elementsubstrate is airtightly sealed, and FIG. 9B is a sectional view taken online A-A′ of FIG. 9A. Reference number 801 represents a source drivingside circuit, which is illustrated by dot lines; reference number 802, apixel section; reference number 803, a gate side driving circuit;reference number 804, a sealing substrate; and reference number 805, asealing agent. The inside surround by the seal agent 805 is a space 807.

Through wirings (not illustrated) for transmitting signals inputted tothe source side driving circuit 801 and the gate side driving circuit803, video signals or clock signals are received from a flexible printcircuit (FPC) 809, which is an external input terminal. The state thatthe FPC is connected to the light emitting panel is shown herein. In thepresent specification, any module on which integrated circuits (ICs) aredirectly mounted is referred to as a light emitting device.

Referring to FIG. 9B, the following will describe the sectionalstructure of the light emitting panel illustrated in FIG. 9A. The pixelsection 802 and the driving circuit portion are formed above a substrate810. The pixel section 802 is composed of pixels, each of which includesa current-controlling TFT 811 and an anode 812 connected electrically toits drain. The driving circuit portion is composed of a CMOS circuitwherein an n-channel type TFT 313 and a p-channel type TFT 814 arecombined with each other.

Banks 815 is formed at both sides of each of the anodes 812. Thereafter,an organic compound layer 816 and cathodes 817 are formed on the anodes812 to produce light emitting elements 818.

The cathodes 817 function as a wiring common to all of the pixels, andare electrically connected to the FPC 809 through a wiring 808.

The sealing substrate 804 made of glass is stuck to the substrate 810with the sealing agent 805. As the sealing agent 805, an ultravioletsetting resin or thermosetting resin is preferably used. If necessary, aspace composed of a resin film may be disposed in order to keep aninterval between the sealing substrate 804 and the light emittingelements 818. An inert gas such as nitrogen or rare gas is filled intothe space 807 surrounded by the sealing agent 805. It is desired thatthe sealing agent 805 is made of a material whose water- oroxygen-permeability is as small as possible.

By putting the light emitting elements airtightly into the space 807 inthe above-mentioned structure, the light emitting elements can becompletely shut off from the outside. As a result, it is possible toprevent the deterioration of the light emitting elements by watercontent or oxygen from the outside. Accordingly, a light emitting devicehaving high reliability can be yielded.

The structure of this embodiment may be combined with the structure ofEmbodiment 1 to 10 at will.

Embodiment 12

FIG. 10A more specifically illustrates the top face structure of thepixel section of the light emitting device produced using the presentinvention and described as FIG. 10A, and FIG. 10B illustrates a circuitdiagram thereof. Referring to FIGS. 10A to 10B, a switching TFT 704 iscomposed of the switching (n-channel) TFT 1002 as illustrated in FIG. 6.Accordingly, about the structure thereof, the description on theswitching (n-channel) TFT 1002 should be referred to. A wiring 703 is agate wiring for connecting gate electrodes 704 a and 704 b of theswitching TFT 704 electrically with each other.

In this embodiment, a double gate structure, wherein two channel formingregions are formed is adopted. However, a single gate structure, whereinone channel forming region is formed, or a triple gate structure,wherein three channel forming regions are formed, may be adopted.

The source of the switching TFT 704 is connected to a source wiring 715,and the drain thereof is connected to a drain wiring 705. The drainwiring 705 is electrically connected to a gate electrode 707 of thecurrent-controlling TFT 706. The current-controlling TFT 706 is composedof the current-controlling (p-channel type) TFT 1003 in FIG. 6.Therefore, about the structure thereof, the description on the switching(p-channel) TFT 1003 should be referred to. In this embodiment, a singlegate structure is adopted. However, a double gate structure or a triplegate structure may be adopted.

The source of the current-controlling TFT 706 is electrically connectedto a current-supplying line 716. The drain thereof is electricallyconnected to a drain wiring 717. The drain wiring 717 is electricallyconnected to an anode (pixel electrode) 718 illustrated by dot lines.

In this case, a storage capacitor (condenser) is formed in a region 719.The condenser 719 is composed of a semiconductor layer 720 connectedelectrically to the current-supplying line 716, an insulating film (notillustrated) which is formed into the same layer as the gate insulatingfilm, and the gate electrode 707. A capacitor composed of the gateelectrode 707, a layer (not illustrated) that is formed into the samelayer as the first interlayer dielectric, and the current-supplying line716 may be used as a storage capacitor.

The structure of this embodiment may be combined with that ofEmbodiments 1 to 10.

Embodiment 13

Another example of the process steps for producing a light emittingdevice that is different from Example 2 will be described with referenceto FIGS. 23(A) and (B).

The process steps are advanced according to Example 2 until the state ofFIG. 22(A). Thereafter, the TFT substrate is transported into the secondprocessing room, and the anti-electrostatic film is removed by waterwashing. A bank 3938 is then formed as shown in FIG. 23(A). The bank3938 may be covered with an insulating film, such as a silicon nitridefilm, on the surface thereof as similar to Embodiment 2, or inalternative, may be subjected to surface modification by carrying outplasma treatment as similar to Embodiment 8.

A first organic compound layer 3950 formed with a polymer organiccompound is initially formed on the anode 3928 by a spin coating method,a spraying method or the like. The layer is formed with a polymerorganic compound material having a positive hole transporting propertyor a polymer organic compound material having a high positive holemobility. As the polymer organic compound material, polyethylenedioxythiophene (PEDOT) may be used.

A second organic compound layer 3951, such as a light emitting layer andan electron transporting layer, and a cathode 3952, which are to beformed thereon, may be formed in the similar manner as in Embodiment 1.

As shown in FIG. 23(B) in detail, the thickness of the first organiccompound layer 3950 can be differentiated between the thickness (t1) onthe anode 3928 and the thickness (t2) on the bank 3938 by appropriatelychanging the viscosity. In other words, the thickness (t1) on the anode3928 can be larger, owing to the concave portion formed from the anode3928 and the bank 3938.

The thickness (t3) at an edge part 3958, at which the anode 3928 and thebank 3938 are in contact with each other, becomes the maximum, and thelayer can be formed to have a certain curvature. According to the form,the covering properties of a second organic compound layer 3951 and acathode 3952 formed as upper layers thereof can be improved.Furthermore, cracking due to stress concentration and electric fieldconcentration are suppressed to prevent the light emitting element fromfailure due to deterioration and short circuit.

Embodiment 14

A light emitting device using a light emitting element is self-luminousand therefore is superior in visibility in bright surroundings comparedto liquid crystal display devices and has wider viewing angle.Accordingly, various electronic devices can be completed by using thelight emitting device of the present invention.

Examples of electronic appliance employing a light emitting device ofthe present invention are: a video camera; a digital camera; a goggletype display (head mounted display); a navigation system; an audioreproducing device (car audio, an audio component, and the like); alaptop computer; a game machine; a portable information terminal (amobile computer, a cellular phone, a portable game machine, anelectronic book, etc.); and an image reproducing device (specifically,an appliance capable of processing data in a recording medium such as adigital versatile disk (DVD) and having a display device that candisplay the image of the data). The light emitting device having a lightemitting element is desirable particularly for a portable informationterminal since its screen is often viewed obliquely and is required tohave a wide viewing angle. Specific example of the electronic devicesare shown in FIGS. 11A to 11H.

FIG. 11A shows a display device, which is composed of a casing 2001, asupporting base 2002, a display unit 2003, speaker units 2004, a videoinput terminal 2005, etc. The light emitting device of the presentinvention is applied can be used for the display unit 2003. The lightemitting device having a light emitting element is self-luminous anddoes not need a backlight, so that it can make a thinner display unitthan liquid crystal display devices can. The term display deviceincludes every display device for displaying information such as one fora personal computer, one for receiving TV broadcasting, and one foradvertisement.

FIG. 11B shows a digital still camera, which is composed of a main body2101, a display unit 2102, an image receiving unit 2103, operation keys2104, an external connection port 2105, a shutter 2106, etc. The digitalcamera is formed by using the light emitting device of the presentinvention to the display unit 2102.

FIG. 11C shows a laptop computer, which is composed of a main body 2201,a casing 2202, a display unit 2203, a keyboard 2204, an externalconnection port 2205, a pointing mouse 2206, etc. The laptop computer isformed by using the light emitting device of the present invention tothe display unit 2203.

FIG. 11D shows a mobile computer, which is composed of a main body 2301,a display unit 2302, a switch 2303, operation keys 2304, an infrared rayport 2305, etc. The mobile computer is formed by using the lightemitting device of the present invention to the display unit 2302.

FIG. 11E shows a portable image reproducing device equipped with arecording medium (a DVD player, to be specific). The device is composedof a main body 2401, a casing 2402, a display unit A 2403, a displayunit B 2404, a recording medium (DVD) reading unit 2405, operation keys2406, speaker units 2407, etc. The display unit A 2403 mainly displaysimage information whereas the display unit B 2404 mainly displays textinformation. The portable image reproducing device is formed by usingthe light emitting device of the present invention to the display unitsA 2403 and B 2404. The term image reproducing device equipped with arecording medium includes video game machines.

FIG. 11F shows a goggle type display (head mounted display), which iscomposed of a main body 2501, display units 2502, and arm units 2503.The goggle type display is formed by using the light emitting device ofthe present invention to the display unit 2502.

FIG. 11G shows a video camera, which is composed of a main body 2601, adisplay unit 2602, a casing 2603, an external connection port 2604, aremote control receiving unit 2605, an image receiving unit 2606, abattery 2607, an audio input unit 2608, operation keys 2609, etc. Thevideo camera is formed by using the light emitting device of the presentinvention to the display unit 2602.

FIG. 11H shows a cellular phone, which is composed of a main body 2701,a casing 2702, a display unit 2703, an audio input unit 2704, an audiooutput unit 2705, operation keys 2706, an external connection port 2707,an antenna 2708, etc. The cellular phone is formed by using the lightemitting device of the present invention to the display unit 2703. Ifthe display unit 2703 displays white characters on a black background,power consumption of the cellular phone can be reduced.

If the luminance of light emitted from organic materials is increased infuture, the light emitting device having an organic element can be usedalso in a front or rear projector in which light bearing outputted imageinformation is magnified by a lens or the like to be projected on ascreen.

The electronic device given in the above often displays informationdistributed through electronic communication lines such as Internet andCATV (cable television), especially, animation information withincreasing frequency. The light emitting device having a light emittingelement is suitable for displaying animation information since organicmaterials have fast response speed.

In the light emitting device, portions that emit light consume power.Therefore it is desirable to display information such that as smallportions as possible emits light. Accordingly, if the light emittingdevice is used for a display unit that mainly displays text informationsuch as a portable information terminal, in particular, a cellularphone, and an audio reproducing device, it is desirable to assign lightemitting portions to display text information while portions that do notemit light serve as the background.

As described above, the application range of the light emitting deviceto which the present invention is applied is very wide and electronicappliance of every field can employ the device. The electronic appliancein this embodiment can be completed by using the light emitting devicemanufactured by implementing the method shown in Embodiments 1 to 13.

By applying the present invention, cracking of an anode is reduced andtherefore degradation of a light emitting element can be prevented. Thepresent invention also includes leveling the surface of the anode,thereby increasing the current density in an organic compound layer. Asa result, the drive voltage can be lowered and the lifetime of the lightemitting element can be prolonged.

Moreover, the invention is capable of moving a substrate between aprocessing room for forming a TFT substrate and a processing room forforming a light emitting element that are physically separated from eachother without causing degradation of TFT characteristics orelectrostatic discharge damage. The structure of the present inventioncan solve the problems of contaminating the TFT with an alkaline metalused as a material of the light emitting element and of degrading thelight emitting element with moisture or gas, and therefore can providean excellent light emitting device.

What is claimed is:
 1. A light emitting device comprising: an insulatingfilm over a substrate; a first electrode over the insulating film; afirst organic compound layer over the first electrode; a second organiccompound layer over and in contact with the first organic compoundlayer; and a second electrode over the second organic compound layer,wherein the first organic compound layer comprises a first region havinga first thickness and a second region having a second thickness, whereinthe first thickness is larger than the second thickness, and wherein thesecond organic compound layer comprises a light emitting layer.
 2. Thelight emitting device according to claim 1, further comprising a bankcovering an edge of the first electrode, wherein part of the firstorganic compound layer is provided over the bank, wherein the firstregion and the first electrode overlap each other, and wherein thesecond region and the bank overlap each other.
 3. The light emittingdevice according to claim 2, wherein a third thickness of the firstorganic compound layer at an edge part, at which the first electrode andthe bank are in contact with each other, is larger than the firstthickness and the second thickness.
 4. The light emitting deviceaccording to claim 1, further comprising a transistor between thesubstrate and the insulating film.
 5. The light emitting deviceaccording to claim 1, wherein the second organic compound layer overlapsthe first region, and wherein the second organic compound layer does notoverlap the second region.
 6. An electronic device comprising the lightemitting device according to claim
 1. 7. A light emitting devicecomprising: an insulating film over a substrate; a first electrode overthe insulating film; a first organic compound layer comprising polymerorganic compound over the first electrode; a second organic compoundlayer over the first organic compound layer; and a second electrode overthe second organic compound layer, wherein the second organic compoundlayer comprises an organic compound having a smaller molecular weightthan the polymer organic compound, wherein the first organic compoundlayer comprises a first region having a first thickness and a secondregion having a second thickness, and wherein the first thickness islarger than the second thickness.
 8. The light emitting device accordingto claim 7, further comprising a bank covering an edge of the firstelectrode, wherein part of the first organic compound layer is providedover the bank, wherein the first region and the first electrode overlapeach other, and wherein the second region and the bank overlap eachother.
 9. The light emitting device according to claim 8, wherein athird thickness of the first organic compound layer at an edge part, atwhich the first electrode and the bank are in contact with each other,is larger than the first thickness and the second thickness.
 10. Thelight emitting device according to claim 7, further comprising atransistor between the substrate and the insulating film.
 11. The lightemitting device according to claim 7, wherein the second organiccompound layer overlaps the first region, and wherein the second organiccompound layer does not overlap the second region.
 12. The lightemitting device according to claim 7, wherein the first organic compoundlayer comprises at least one of a hole injecting layer and a holetransportation layer, and wherein the second organic compound layercomprises a light emitting layer and an electron transportation layer.13. The light emitting device according to claim 7, wherein the polymerorganic compound is polyethylene dioxythiophene.
 14. An electronicdevice comprising the light emitting device according to claim
 7. 15. Alight emitting device comprising: an insulating film over a substrate; afirst electrode over the insulating film; a bank covering an edge of thefirst electrode; a first organic compound layer comprising polymerorganic compound over the first electrode and the bank; a second organiccompound layer comprising a light emitting layer over the first organiccompound layer; and a second electrode over the second organic compoundlayer, wherein the second organic compound layer comprises an organiccompound having a smaller molecular weight than the polymer organiccompound, and wherein the first organic compound layer has a curvedupper surface at an edge part at which the first electrode and the bankare in contact with each other.
 16. The light emitting device accordingto claim 15, wherein the first organic compound layer comprises a firstregion having a first thickness and a second region having a secondthickness, and wherein the first thickness is larger than the secondthickness.
 17. The light emitting device according to claim 16, whereinthe second organic compound layer overlaps the first region, and whereinthe second organic compound layer does not overlap the second region.18. The light emitting device according to claim 15, further comprisinga transistor between the substrate and the insulating film.
 19. Thelight emitting device according to claim 15, wherein the first organiccompound layer comprises at least one of a hole injecting layer and ahole transportation layer, and wherein the second organic compound layercomprises an electron transportation layer.
 20. The light emittingdevice according to claim 15, wherein the polymer organic compound ispolyethylene dioxythiophene.
 21. The light emitting device according toclaim 15, wherein the first organic compound layer is formed by a spincoating method or a spraying method, and wherein the second organiccompound layer is formed by an evaporation method.
 22. An electronicdevice comprising the light emitting device according to claim 15.